A NUMERICAL SIMULATION STUDY OF THE IMPACTS OF SURFACE ALBEDO ON THE SUMMER TIME NORTH AFRICA SUBTROPICAL HIGH

Two sets of numerical experiments different in surface albedo were carried out by using of LASG L9R15 AGCM in this work. The impacts of surface albedo on the summer time North Africa subtropical high are investigated through comparative study of the July mean climate of these two sets of experiments. The results in dicate that with the increase of surface albedo, especially at North Africa, the netradiation reaches the ground surface decreases (from 140W/m2 to 101W/m2), so do the surface temperature and the sensible heat flux transfered to the above atmosphere, therefore the convection and precipitation in North Africa reduce. The cooling of middle and lower troposphere in the aforementioned region results in more convergence at high level and more divergence at low level, hence stronger downward motion and the reinforcement of the North Africa subtropical high during summer time.Besides the aforementioned impacts of the changes of surface albedo on local climate in north Africa, the differential circulation in north Africa enhances the low level convergence and high level divergence in south Asia through divergent wind circulation which connects these two regions, therefore strengthens the South Asia high to some extent, and increases monsoon precipitation in southeastasia.